In modern societies, multimedia in daily life is rapidly developing and ITS (Intelligent Transport Systems) such as the ETC device used in toll roads and the GPS is becoming widely used. In order to treat the extraordinary increase of information and telecommunications technologies, the frequency of signals used for transmission is increasing.
As material used for the information communication devices employing such a high frequency, engineering plastics which exhibit excellent dielectric properties in high frequency regions (especially in gigahertz bands) are attracting attention. The engineering plastics also exhibit good productivities and lightweight properties and, therefore, they are expected to be applied in the manufacture of chassis and packages of communication devices and electronic devices as well as in that of dielectric bodies and the like.
Among the engineering plastics, thermotropic liquid-crystalline polyester resin (hereinafter called liquid-crystalline polyester resin or LCP) has the following excellent properties and is especially expected to be suitable for manufacturing devices which use high-frequency signals:
(1) excellent dielectric properties: the relative permittivity (∈r) is constant in the frequency regions employed and dielectric loss tangent (tan δ) is small,
(2) good physicality: mechanical properties including low-expansion property (dimensional stability), heat-resistance, flame-retardancy and rigidity are good, and
(3) good molding flowability: which allows processing of molded articles having down-sizing and thinner parts.
Among the liquid-crystalline polyester resins, liquid-crystalline polyesters comprising a large amount of a repeating unit derived from 6-hydroxy-2-naphthoic acid which is one of aromatic hydroxy carboxylic acid have been recently proposed in terms of their good heat-resistance and dielectric properties.
Though the liquid-crystalline polyesters comprising a large amount of a repeating unit derived from 6-hydroxy-2-naphthoic acid as aromatic hydroxycarboxylic acid (Japanese Patent Application laid open No. 2004-196930 corresponding to U.S. Pat. No. 7,063,892 and Japanese Patent Application laid open No. 2007-154169) exhibit excellent dielectric properties, their impact strength is relatively poor and, therefore, they are unsuitable for use in parts of a mobile phone or the like which tend to be impacted through being dropped in daily use.
With regard to a liquid-crystalline polyester resin disclosed in Japanese Patent Application laid open No. 2002-179776 (U.S. Pat. No. 6,815,526) which is obtained from a large amount of 6-hydroxy-2-naphthoic acid and a small amount of p-hydroxybenzoic acid as aromatic hydroxycarboxylic acids, it has a problem in relation to molding processability because it exhibits a high melting temperature.
In order to provide a liquid-crystalline polyester resin which exhibits good impact strength and molding processability, the present inventors conducted studies on liquid-crystalline polyesters which comprise a large amount of 6-hydroxy-2-naphthoic acid, and found that a liquid-crystalline polyester blend obtainable by combining a liquid-crystalline polyester which comprises a large amount of 6-hydroxy-2-naphthoic acid and a liquid-crystalline polyester which is obtainable by using a certain amount of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid as monomers exhibits good impact strength and molding processability (Japanese Patent Application laid open No. 2009-108191 corresponding to US Patent Application Publication No. 2009-111926).
However, though the liquid-crystalline polyester blend exhibit good mechanical and thermal properties when fillers such as glass fiber are admixed, their mechanical and thermal properties tend to be impaired when fillers with good dielectric properties such as calcium titanate and the like are admixed.